This invention is directed to a device which provides an illuminated, floating bar graph type display. The length of the illuminated bar as well as its floating or relative position are used to indicate plural or multiple characteristics of a complex electrical waveform. By "floating bar" is meant a group of illuminated segments in which both ends of the group may move, but not necessarily in unison. A "segment" as used herein is an art term meaning an individual light source, normally an LED (light emitting diode). The invention provides a rapidly and easily interpreted visual display of multiple electrical characteristics of a complex waveform.
The invention is particularly well suited for audio signal monitoring or analysis. In this sense it is related to my previous U.S. Pat. No. 4,166,245 of Sep. 28, 1979 which is incorporated herein by reference. The logic circuit means of the prior patent functions to illuminate a segment if the both the peak and RMS values exceed the bias values and when only the peak values exceed the bias values, to illuminate that single segment corresponding to the maximum value LED. The display, then, is difficult to read as to meaning because one must constantly keep in mind that whereas an LED may be illuminated because both the peak and RMS outputs exceed the bias voltages, another LED may not. As noted in that patent, the RMS or average value of the audio signal waveform provides knowledge of the loudness or apparent volume of an audio-derived input signal while the peak value of the waveform provides useful information vis-a-vis the maximum signal handling capability of the audio signal processing equipment or the saturation characteristics of the medium, a magnetic tape for example, on which the audio signal is being stored. In contrast to my prior patent, however, this invention discloses and claims wholly different logic means which functions to provide the illuminated, floating bar graph type display. In common with my prior patent, this invention utilizes sources of peak voltage and RMS voltage and a pair of comparators associated with each LED, and a bank of voltage-dividing resistors for providing the ascending scale of voltages represented by the individual LEDs.
As noted, the logic means of this invention functions to provide an illuminated, floating bar graph type display. The floating bar is an "open ended" bar of illuminated segments, in which the maximum value segment of the bar indicates peak voltage, the particular segment (not illuminated) next to the minimum value segment of the bar indicates RMS voltage. When using a logarithmic scale the number of segments of the bar is indicative of the crest factor (peak-to-average ratio). The illuminated segments therefore simultaneously display easily read and meaningful knowledge of three useful characteristics of an audio signal.
This invention relates to an electrical metering device of the linear type employing a floating bar of segments and logic means controlling the length and position of the bar within its possible upper and lower limits so that the upper limit extremity of the bar expresses knowledge of one electrical characteristic, the lower limit extremity of the bar expresses knowledge of another electrical characteristic, and the length of the bar between these limits expresses knowledge indicative of the ratio of these limits. The floating bar is preferably formed by a linear array of discrete and separated segments or indicators capable of illumination, preferably light emitting diodes (LEDs), depicting increasing electrical values from one end of the array to the other.
The invention is capable of simultaneously displaying three related electrical characteristics of an audio signal, namely the peak amplitude of the audio signal, the RMS or average value of the magnitude of the audio signal and the crest factor or peak-to-average ratio of the audio signal.
An object of the invention, therefore, is to provide a novel display for plural electrical characteristics of a complex waveform wherein the display involves a group of illuminated segments whose opposite ends are indicative of two different but related electrical characteristics of the same waveform and whose length is an indication of a third characteristic of that same waveform.
Basically, the invention involves a bank of first comparators and a bank of second comparators having first inputs connected to different voltage-divided fixed value inputs and with the first comparators having a second input all connected to a peak voltage value of the waveform and with the second comparators having a second input all connected to a RMS or average voltage value of the waveform. The first comparators have an output signal (a logical "one") only when the peak signal input to those comparators exceeds the bias voltage and this output signal is connected as one input to an output AND gate. The second comparators have an output signal (a logical "one") only when the RMS signal input to the those comparators exceeds the bias voltage and this output signal is connected to the other input of the output AND gate through an inverter. The output AND gates drive the separate LEDs. A particular output AND gate will not provide a "one" output and thus energize its associated LED unless its associated output inverter also provides a "one" output. Stated otherwise, a particular output AND gate will cause illumination of its associated LED if the comparator connected as one input to the associated output AND gate has a "one" output and the comparator connected through the associated inverter as the other input to the associated inverter as the other input to the associated output AND gate does not have a "one" output. Thus, a particular LED will be illuminated if and only if the peak value exceeds the voltage-divided bias corresponding to that particular LED but the average value does not exceed that of the same voltage-divided bias.
Thus, the invention is characterized by the illumination of LEDs of a linear array thereof as a function of exceeding the peak value and not illuminating them as a function of not exceeding the average value. The result is an illuminated, floating bar graph type display wherein the floating bar represents, at its top LED, the peak value of the waveform and wherein that unlit LED below this bar represents the average value of the waveform. As the values of peak amplitude and average amplitude vary, the bar graph will move or float as the LEDs forming the illuminated segments likewise move and the length of the floating bar may also vary. Regardless of the fineness or coarseness of uniform voltage divisions, the length of the floating bar will always give an indication of the crest factor (peak-to-average ratio) for the waveform. Although there will be no exact correlation under those circumstances between the number of illuminated segment and the crest factor, a better correlation can be achieved by making the scale of the voltage-divided bias voltages logarithmic. Under these conditions, the number of illuminated segments will indicate the crest factor. Accordingly, the three characteristics of peak value, average value and crest factor are simultaneously displayed with this invention.
Other objects and advantages of this invention will become apparent as this description proceeds.